Re: [Patch] Another small memattr fix.

[Andrew Cagney <ac131313 at cygnus dot com>]

> On Jun 14, 12:44pm, Don Howard wrote:
>
>
> > The strings are arbitrary expressions and are converted to address via
> > parse_and_eval_address(), which does not flag overflow:
> >
> > mem_command (char *args, int from_tty)
> > {
> >   CORE_ADDR lo, hi;
> >   char *tok;
> >   struct mem_attrib attrib;
> >
> >   if (!args)
> >     error_no_arg ("No mem");
> >
> >   tok = strtok (args, " \t");
> >   if (!tok)
> >     error ("no lo address");
> >   lo = parse_and_eval_address (tok);
> >
> >   tok = strtok (NULL, " \t");
> >   if (!tok)
> >     error ("no hi address");
> >   hi = parse_and_eval_address (tok);
> >
> > mabe parse_and_eval_address could detect overflow and throw an error().
On real hardware, addresses overflow causes it to wrap.  The problem of 
signed vs unsigned addresses is also lurking in there as well.

From memory there is a tabled proposal to add a CORE_ADDR alu object so 
that CORE_ADDR arrithmetic is correct.


> Maybe I'm missing something, but it seems to me that you're still left
> with the problem of how to represent the maximum address + 1.  (Throwing
> an error doesn't really help, does it?)
>
>
> > Another possiblity is that the interface could be changed, making the
> > upper bound inclusive also. 
>
> This sounds better.
>
> So, on a 16 bit machine, you could say
>
>     mem 0xf000 0xffff ro
>
> to indicate that the top 4096 bytes are read-only.
I can think of three alternatives:

	[base, bound)
	[base, bound]
	[base, base+size-1)

The first one is what the doco says and has been there for a while so I 
don't think that changing it is a good idea.

Internally, I suspect base+size-1 is the best representation.  However, 
for the user interface, is there anything that really says that:

	mem 0xfffffff0 0

is either illegal or poorly defined?  Perhaphs allow that and not stuff 
like:

	mem 0xfffffff0 0xffffffff0

Andrew